Nowadays there are available terminals that operate in various different frequency bands. Such terminals have greater performance and, in comparison with older terminals, are better adapted to take advantage of the new services appearing for the terminals all the time.
Terminals adapted for multi-frequency usage may be utilized in those wireless communications networks where the operations have been adapted in advance to function together with the terminals.
For each wireless communications system a previously determined frequency band is assigned for transmission and reception of signals. Wireless communications systems using different frequency bands include for example: digital 2G telecommunications networks, such as GSM (Global Systems for Mobile Telecommunication), DCS (Digital Cellular System), PCS (Personal Communications Services) and 3G UMTS (Universal Mobile Telecommunications System).
DCS and PCS networks are based on GSM technology. UMTS networks in Europe are based on WCDMA (Wideband Code Division Multiple Access) technology. The technology corresponding to 3G UMTS in USA is called CDMA2000.
Subscriber terminal applying wireless data transfer normally consists of at least one antenna for transmission and reception of signals. Placing a single large antenna in the terminal or inside the covering frame may be difficult or even impossible in practice. This is because it might require excessive growth of the physical size of the terminal, which is to be avoided at all cost. With a single antenna it is not possible to achieve a good enough performance in relation to the physical size, in comparison with the multi-band devices using multiple optimised antennas.
One implementation of an antenna arrangement adapted for usage in a multi-band environment is described in the patent publication WO 02/07254. The antenna arrangement tries to accomplish a good barrier damping between single frequency bands and to enable, without active components, separate and self-sufficient radiation curves as well as a large decoupler connection between the frequency bands. According to the publication, this will be accomplished by separating filters utilising frequency-selective filter structure. The filter structure supplied with sufficient barrier damping al-lows dividing the frequency band into two sub-bands. On the one hand, each separating filter combines two signals of different frequencies into one signal, and on the other divides the frequency band coming from the antenna into two frequency bands for two branches. There are always twice as many radiators as there are frequencies. This kind of antenna arrangement is not flexible because the amount of antennas is bound to the amount of frequencies. In addition, since the circuitry of the antenna arrangement is fixed, the filter structure requires a relatively large quantity of filters.